Ocean wave energy, especially in more northern and southern latitudes of the globe, is several times more concentrated than the wind energy which produces ocean waves, wind energy itself being several times more concentrated than the solar energy which produces wind. Wave energy, a huge global resource, is also more consistent and predictable than solar or wind energy. Wave energy, therefore, has the potential to become less costly than solar or wind. The wave energy industry, however, remains in a nascent state, well behind solar and wind in spite of (or perhaps in part because of) a profusion of hundreds of proposed unique distinct wave energy converter (WEC) designs, and because no one has yet demonstrated a WEC design which is generally recognized as ocean survivable with a levelized cost of power competitive with solar and wind.
Most proposed WEC designs attempt to absorb wave energy from above with horizontal plane surface area dependent WECs including spar buoys, articulating rafts, and oscillating water columns (OWCs). Because typical ocean waves and swells average 100-300 meters in wave length, such horizontal plane surface area dependent WECs must at least span wave crests (¼ of total wave length) requiring WECs with huge surface area making them unaffordable. Compounding this high surface area WEC cost problem, most surface area dependent WECs capture only “heave” (the vertical or potential wave energy component) and little or no “surge” (lateral or kinetic energy component), each being exactly ½ of total wave energy in deep water (depths above ½ wave length). Wave energy is much more concentrated as it passes through a vertical plane at or near the water surface and parallel to oncoming wave fronts. Wave energy decreases exponentially with water depth.
The present disclosure is of the wave “barrier” or “terminator” type WEC utilizing at least one “Elongated Wave Front Parallel” (EWFP) surface float. Other terminator type WECs include the “Salter Duck” (Stephen Salter, U. of Edinburgh, GB1482085, 1977), Akers Engineering barge with float (Ersdal, WO 2011071390), Columbia StingRay (Rhinefrank US 2015/0252777), Azura (Gardiner US2010/01409440), WEPTOS (Larsen WO2015082638), and the related John Rohrer/Rohrer Technologies, Inc. patents and applications (referenced above in the Cross-reference to Related Applications section).
The Salter “Duck” (FIG. 1) uses multiple adjacent very large diameter EWFP floats of circular section with a large buoyant cam lobe shaped protrusion extending from one quadrant and facing towards prevailing oncoming wave fronts. The float lobe rotates or “nods” up and down (like a “duck”) up to about +/−45° about a large diameter relatively motion stabilized cylindrical core or “flexible spine” in response to wave heave and surge forces driving a hydraulic power take-off (PTO) system located within the core. Projected wave energy capture efficiencies (in realistic random seas) are promising (up to 65%) with large float diameter ducks (18 meters) projected to capture 1.5 to 3.0 times more wave energy than smaller diameter (6 meter) Ducks but even at 6 meter float diameter capital costs/MW appear uncompetitive with other renewables (Nature Vol. 263, No. 5574, pp. 2230226, Sep. 16, 1976).
The WEPTOS WEC consists of multiple adjacent Salter Duck shaped floats mounted concentrically about either of 2 line shafts (drive shafts) arranged in a “V” configuration with the apex pointed up-sea toward oncoming wave fronts. Wave forces successively lift the buoyant cam shaped lobes of each Duck shaped float rotating each line shaft (which is connected to a generator or other PTO) in only one direction. The floats gravity return into subsequent wave troughs without power capture using a ratcheting or one way clutch connection to the line shaft.
The Aker WEC consists of an up-sea EWFP float attached below the Still Water Line (SWL) to a down-sea stabilizing barge with 2 swing or PTO drive arms. The barge is several times the volume, mass, and cost of the EWFP float resulting in high capital cost (CAPEX).
The Columbia StingRay (FIG. 2 and 2015/0252777), like the Salter Duck, also utilizes a large central cylinder (8 meter diameter) housing its 2 direct drive rotary electric PTO(s), with a fore float similar in shape to the Duck cam lobe shaped float. Unlike the Duck, however, only the float rotates rather than the entire cylinder (on 2 swing arms about pivot points on the central cylinder horizontal axis). The forward oriented cam shaped lobe or float of the StingRay rotates about a stationary central cylinder rather than being affixed to a rotating central cylinder. The cylinder is rigidly mounted to a vertically oriented twin spar column frame reaching deep into the water column and connected to each other near the bottom by a horizontal plane drag plate to reduce cylinder heave (vertical) motion, the two frame vertical columns being connected to a submerged mooring buoy allowing the WEC to weather vane parallel to oncoming wave fronts, both frame and mooring as previously described in Rohrer U.S. Pat. No. 8,604,631 and its continuations.
The StingRay also utilizes a rear EWFP float on swing arms (like McCabe U.S. Pat. No. 5,132,550) which is partially masked from wave energy by the large central cylinder in front of it. During severe seas, the fore float is either rotated behind the cylinder using it as a protective barrier or flooded and submerged as previously described and claimed in Rohrer U.S. Pat. No. 8,614,520 and its continuations.
The Azura (formerly WET-NZ) WEC (US 2010/0140944) utilizes a narrow (point absorber type) horizontally oriented float, hinged near the water surface to a vertically oriented “elongate reactive body”. It differs from Salter's Duck, WEPOS, the Stingray. Akers, and the present disclosure by arranging the float to trail rather than precede the reactive body (buoyant cylinder, barge or frame). The wave surge forces acting against both the upper portions of the reactive body and the float produce both lateral movement and rotation of the body enhancing the relative motion between float and body (frame). Such lateral and rotational movement of any such vertically oriented elongated reactive body connected to a surface float is impossible to prevent. The Stingray (Rhinefrank 2015/025277, however, does claim lateral and rotation movement of their buoyant cylinder and twin spar frame which is predated by Azura. McCabe. and others.
The RTI F2 QD of the present disclosure utilizes swing arms to rotatably attach the at least one EWFP float to its twin spar heave stabilized (but not pitch stabilized) frame driving a single or dual PTOs housed within the frame, thus avoiding the costly central cylinder of the Duck and Stingray. Preferred embodiments of the present and the referenced John Rohrer Related U.S. Patents and Application Data describe and claim submergence of the EWFP float(s) below the troughs of storm waves, by seawater flooding or other means, for secure WEC survival in severe sea conditions.